The spinning of concrete is a process in which concrete mixture is moulded and compacted under the action of the centrifugal force arising during the fast rotational motion of the mould around its longitudinal axis. As a result of the spinning of the liquid concrete mixture, an element annular in cross section, characterised by an inhomogeneous layered wall structure, is produced. The heavier constituents tend towards the cross-section wall’s outer side, while the lighter components tend towards its inner side. The way in which the particular constituents are distributed in the element’s cross section is of key importance for the macro properties of the manufactured product. This paper presents procedures for investigating spun concrete and interpreting the results of such investigations, which make it possible to characterise the microstructure of the concrete. Three investigative methods were used to assess the distribution of the constituents in the cross section of the element: micro-computed tomography (µCT), 2D imaging (using an optical scanner) and nanoindentation. A procedure for interpreting and analysing the results is proposed. The procedure enables one to quantitatively characterise the following features of the microstructure of spun concrete: the mechanical parameters of the mortar, the aggregate content, the pore content, the cement paste content, the aggregate grading and the size (dimensions) of the pores. Special attention is devoted to the determination of the variation of the analysed quantities in the cross section of the element. The result of the application of the investigative procedures is presented for an exemplary spun concrete element. The proposed procedures constitute a valuable tool for evaluating the process of manufacturing spun concrete elements.

Impact of geotechnical works related to plunging piles in the ground and modification of the condition of the soil foundation for concrete in the early stage of its bonding, and influence on adhesion of reinforcing steel to concrete can determinate the target capacity of a reinforced concrete structure. Impact of vibrations testing on bond strength is only possible on real designs or models subjected to dynamic impact. The paper presents mechanisms of adherence reduction caused by relative displacement of reinforcing steel and concrete. Moreover, dynamic influences (frequencies and vibration velocities) measured on structures within and around construction sites, where geotechnical works were carried out were also compared. Data obtained after their statistical analysis might become the basis for modelling an experiment.

Taking into account the possibilities offered by two imaging methods, X-ray microcomputed tomography (µCT) and two-dimensional optical scanning, this article discusses the possibility of using these methods to assess the internal structure of spun concrete, particularly its composition after hardening. To demonstrate the performance of the approach based on imaging, laboratory techniques based on physical and chemical methods were used as verification. Comparison of obtained results of applied research methods was carried out on samples of spun concrete, characterized by a layered structure of the annular cross-section. Samples were taken from the power pole E10.5/6c (Strunobet-Migacz, Lewin Brzeski, Poland) made by one of the Polish manufacturers of prestressed concrete E-poles precast in steel molds. The validation shows that optical scanning followed by appropriate image analysis is an effective method for evaluation of the spun concrete internal structure. In addition, such analysis can significantly complement the results of laboratory methods used so far. In a fairly simple way, through the porosity image, it can reveal improperly selected parameters of concrete spinning such as speed and time, and, through the distribution of cement content in the cross-section of the element, it can indicate compliance with the requirement for corrosion durability of spun concrete. The research methodology presented in the paper can be used to improve the production process of poles made of spun concrete; it can be an effective tool for verifying concrete structure.

In view of location and tight work schedule of civil projects, more and more frequently the various kinds of work overlap each other in space and time. Hence, their interactions need to be anticipated. An example of such works are pile driving which generate vibrations, which begs a question whether and to what extent they affect proper operation of other structures being constructed at the same time, e.g. reinforced concrete elements. This paper deals with the problem of steel-to-concrete adherence in reinforced concrete elements by providing mechanism of adherence destruction, methods use to determine adherence stresses and outlining analytical and numerical methods. Examinations on how vibrations affect fresh concrete mix are provided in the latter part of the paper. At the end, further direction for development is discussed.

Is the variation in the compressive strength of concrete across the thickness of horizontally cast elements negligibly small or rather needs to be taken into account at the design stage? There are conflicting answers to this question. In order to determine if the compressive strength of concrete varies across the thickness of horizontally cast elements, ultrasonic tests and destructive tests were carried out on core samples taken from a 350 mm thick slab made of class C25/30 concrete. Special point-contact probes were used to measure the time taken for the longitudinal ultrasonic wave to pass through the tested sample. The correlation between the velocity of the longitudinal ultrasonic wave and the compressive strength of the concrete in the slab was determined. The structure of the concrete across the thickness of the slab was evaluated using GIMP 2.10.4. It was found that the destructively determined compressive strength varied only slightly (by 3%) across the thickness of the placed layer of concrete. Whereas the averaged ultrasonically determined strength of the concrete in the same samples does not vary across the thickness of the analyzed slab. Therefore, it was concluded that the slight increase in concrete compressive strength with depth below the top surface is a natural thing and need not be taken into account in the assessment of the strength of concrete in the structure.

This paper describes a study of the chloride content in the concrete lagging of prestressed concrete elements of the roof structure of an aluminium foundry building. Sources of chloride pollution in industrial facilities are discussed. Methods for collecting dust deposited on the structure and sampling concrete for chloride concentration testing are presented in detail. The test methods used and the apparatus used to assess the chloride content at the thickness of concrete reinforcement lagging are presented. Investigations of the chloride content in the concrete of the reinforcement cover showed a very high concentration of chloride in the near-surface layer, depending on the location of the element in relation to the source of chloride emission into the environment. In contrast, the concrete of the deeper layers of the lagging contained very small amounts of Cl⁻ chlorides. The results of the chloride content of the lagging concrete were plotted against the distance from the surface of the specimen and approximated by the function C(x,t) based on Fick’s second law and its solution. A satisfactory fit of the course of this function to the experimental results was obtained. Based on the obtained C(x,t) function, the durability of the main structural components of an aluminium foundry industrial hall operating in a chloride environment was estimated.